The cataracts resulting from IR exposure are compared with those linked to UV exposure. The IR exposure produces changes in the lens proteins, the crystallins, while UV exposure seems to attack specific amino acids. Gel electrophoresis of lens proteins have been used to detect the earliest changes possible in cataract formation following exposure to IR from broad band and laser source irradiation. Cataracts can be easily formed in rabbit lenses in vivo when the laser radiation is restricted to the lens alone at power levels above 1 W for 1 minute. Lower power levels do not produce immediate cataracts but changes in lens proteins can be detected by thin layer isoelectric electrophoresis of plain polyacrylamide gels and with sodium dodecyl sulfate (SDS) or 6 M urea. The plain gels (pH 3.5 to 10) showed a decrease in the a crystallins indicating a possible change of soluble a crystallin to an insoluble high molecular (HM) weight form. However, small amounts of Q and y crys-tallins may also be involved in the formation of a HM insoluble aggregate. Soluble HM weight crystallins often were detected as the a crystallin disappeared. This HM soluble fraction may be an intermediate step in the process in forming insoluble a crystallin. Following higher laser power levels the crystallin has a markedly decreased mobility which also might be a precursor for the insolubilization of all crystallins. Similar changes in the lens proteins are seen following broadband IR exposure in vivo, or in vitro. Lenses incubated in vivo at various temperatures showed some, but not an, of the same changes. The IR exposure can be considered an acceleration of the aging process.